Patent application document US 2011/0282508 (D1) describes a system for control of a power grid (PTDG in D1). The system may control the power in the grid by means of for example a substation and a transformer (see claim 1 of D1). The system is aimed at identifying operational states of equipment, identify abnormal conditions and select actions to be taken (see claims 2-4 of D1). The system is further configured to perform simulations of at least a part of the power grid (PTDG) (see claim 6 of D1), and use criteria for selecting actions in order to modify the operation of equipment of the power grid (see claim 7 of D1). The system is provided to operate equipment in an overloaded condition. For example, the system can receive a request for overload of a transformer, from a grid operator, and perform a simulation to determine whether or not the request can be granted (see § 0071 of D1). In order to perform such a simulation, the system includes a transformer monitoring system (see § 0016 of D1) and may determine the health of the transformer (§ 0064), and perform a diagnosis of the transformer (§ 0067). As a result of monitoring and diagnosis, the system may also determine that service or maintenance is needed.